As a power source for driving a motor of a hybrid automobile, etc., a secondary battery such as a nickel hydrogen battery and lithium ion battery is currently being used.
At the time of charging of such a secondary battery, overcharge must be avoided so as to suppress, for example, heat generation of the secondary battery or deterioration of the performance. A secondary battery system usually has a function of avoiding overcharge.
For example, Patent Document 1 discloses a secondary battery system using a liquid electrolyte, such as nickel hydrogen battery. In the secondary battery system disclosed in Patent Document 1, when a gas pressure in a battery case increases, the battery is judged to be in an overcharge state, and the charging is stopped.
Patent Document 2 discloses a secondary battery system in which a laminate material obtained by laminating together a metal foil such as aluminum and a heat-welding resin layer via an adhesive layer is used for the outer package. In this outer package, a stacked battery having stacked therein an anode current collector layer, an anode active material layer, an electrolyte layer, a cathode active material layer, and a cathode current collector layer is housed to form a sealed battery. Then, sealed batteries are stacked in the thickness direction to form an assembled battery.
In the secondary battery system disclosed in Patent Document 2, when a contact pressure between adjacent sealed batteries or between a sealed battery and a member constraining the sealed battery in the thickness direction is elevated, the battery is judged to be in an overcharge state, and the charging is stopped. In Patent Document 2, it is disclosed that the outer package of the sealed battery is expanded by a gas produced upon decomposition of a liquid electrode and this results in a rise in the contact pressure between outer packages of adjacent sealed batteries or between an outer package of a sealed battery and a member constraining the sealed battery in the thickness direction.
Patent Document 3 discloses an all-solid-state secondary battery system using a stacked or wound battery in which an anode current collector layer, an anode active material layer, a solid electrolyte layer, a cathode active material layer and a cathode current collector layer are stacked or wound. The stacked battery is housed in an outer package to form a sealed battery. In the all-solid-state secondary battery system disclosed in Patent Document 3, a contact pressure sensor is provided inside the stacked battery and when the contact pressure sensed by the contact pressure sensor is elevated, the battery is judged to be in an overcharge state, followed by stopping of charging.